hair cracks in 993 heads

911TE · 03-03-2006, 06:10 AM

In cleaning and bead blasting the heads of my 993 engine I found in every head a very small crack beginning in the threads of only one spark-plug to the exhaust valve seat.
Has anybody here, especially the profi head rebuilder seen this before?
Can I reuse these heads with new valve guides and ignore the cracks or will finally the seat-rings fall out?

Sebastian

paulweir · 03-03-2006, 07:55 AM

I have a set of 993 heads if you need them.

ischmitz · ischmitz's Garage

I'd take them to an experienced machine shop that has dealt with 911 engine parts before. They will be able to advice whether this can be repaird.

911TE · 03-04-2006, 10:51 AM

Paul, thank you for the offer, I`m only afraid shipping them to Germany wouldn`t be cheap. If the experts say they are crap, I´ll come back to you!

ischmitz, I´ve been to my machine shop, he is able to repair them, but this would mean pulling the valve seats, welding, cutting new threads for the plugs, machining for over-size valve seat and pressing in new seats, probably more expensive than used heads.
The machinist says, there are a lot of cylinder heads of other brands where cracks are standard and do not harm, he just doesn`t know how Porsche 993 heads behave!

Sebastian

Speedster94 · 03-04-2006, 11:07 AM

hallo
i send you a email ,i have aset of 993 heads .
harald

paulweir · 03-05-2006, 06:44 AM

Hi Sebastion, Shipping by US Mail is cheaper than you might think and only takes a week, I ship Porsche racing engine parts to Europe quite often.
Thanks, Paul Weir

ChrisBennet · ChrisBennet's Garage

Paul and Harold,
I know you guys must have seen a lot of 911 heads. I'm curious, what is your experience with 993 head cracks or 911 head cracks in general?
-Chris

paulweir · 03-05-2006, 09:56 AM

The only cracked 911-930 heads I can remember seeing came off 935 and 962 IMSA engines where the boost was turned way up.
I have a few cracked 3.8 RSR heads an a few cracked 993 heads but I am sure they came off full race engines so its more understandable.

78-911SC · 03-06-2006, 12:19 PM

Harald please respond to my emails.
Thanks

911TE · 03-06-2006, 01:43 PM

I attach a picture of the crack, highlighted with green color, otherwise it wouldn`t be visible on the picture.

Any comments?

Sebastian

john walker's workshop · 03-06-2006, 03:40 PM

it would probably be cheaper to start with a good set of used heads than repair those. remove seats, weld, remachine, install new seat X 6 wouldn't be particularly cheap. seat swapping in 911 heads is dicey. i've seen too many replaced seats come loose.

Jeff Alton · 03-06-2006, 05:45 PM

Are these the 914 heads of the future?

I wonder if we will start seeing more of this....

Cheers

911TE · 03-07-2006, 06:50 AM

We made a test today at the machine shop, heads were heated in the oven to 300 degrees Celsius=572 degrees Fahrenheit, the exhaust rings are still firmly in the heads. I think I will leave them in and hope!

Sebastian